The Wacky Math Behind Leap Years

leap years
Leap year definition | Image by Frank Brennan/Getty Images

Every four years — with a few exceptions — February 29 appears on the calendar. But why the fuss and does it really fix anything?

This year, February 29 has once again graced the calendar. While the leap year has considerable cultural relevance, such as the Irish custom of women proposing marriage to men on leap day, the scientific rationale is perhaps even more wacky.

The actual science behind the leap year is a bit of a head-scratcher, especially since the mathematical equation behind it actually doesn’t work out perfectly.

Leap years occur every four years to correct the 5-hour, 48-minute, 56-second discrepancy between the calendar year and the astronomical year. While there are 365 days in a regular calendar year, it takes approximately 365.25 days for the Earth to orbit the Sun. In order to avoid the inevitable chaos of astronomical seasons shifting over time, adding an extra day to the calendar helps make up this difference.

Yet those who are strong in math might have noticed that adding an extra day every four years would actually be overkill — resulting in a surplus in the common calendar of over 44 minutes. There are two rules to help compensate for this.

First, a leap year can only occur if it can be evenly divided by 4 — as is the case for 2024. Next, a leap year is skipped if it can be divided by 100 — as was the case for 1900 — unless it is also evenly divisible by 400. This explains why the year 2000 was not skipped over and was considered a leap year. The next leap year to be skipped over is 2100.

True mathematicians might again notice that things don’t quite match up — even with the aforementioned rules, a few seconds are added to the calendar each leap year. This amounts to roughly three extra days every 10,000 years, per the Old Farmer’s Almanac.

While being born on February 29 might be a bit of a drag due to only being able to celebrate properly one’s birthday once every four years or so, the silver lining for “leaplings” is that an entire Leap Year festival is held in their honor in the West Texas town of Anthony, which claims to be the Leap Year Capital of the World.

The 2024 celebration will take place from March 1 to March 2, with barbecue, live music, and more on offer. People with a February 29 birthday can receive a complimentary barbecue dinner at Rollin Smoke BBQ on February 29 in Anthony.

However, for those in the Dallas-Fort Worth area, check out The Dallas Expresslist of opportunities for food deals and more.

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